1. Field of the Invention
The present invention relates to a CRT (Cathode Ray Tube) socket that connects to the base of a CRT used, for example, as a color television set or display monitor. In particular, the invention relates to a construction that is effective in preventing the generation of corona currents between the ends of two focusing terminal pins on a double focus tube and between the end of a focusing terminal pin and the surrounding insulating resin wall.
2. Description of the Related Art
CRTs are widely used in color television sets and display monitors. As the sizes and resolutions of CRTs have increased, double focus tubes have come into widespread use.
Increases in the sizes of color television sets and display monitors have been accompanied by demands for wide-screen displays and displays with reduced depth. Such demands have resulted in higher voltages being applied to CRTs, so that, in a double focus tube, there is a trend toward a higher potential difference across the two focusing terminal pins. Also, to produce a high resolution display across the entire screen, a high-frequency dynamic voltage waveform is superimposed on one of the focusing terminal pins. As CRT display screens become larger, wider and flatter, higher voltages must be applied using such dynamic voltages.
One example of the construction of a conventional CRT socket is shown in FIGS. 8A and 8B. A stem base 103 is attached to the end of the neck of the CRT. Two focusing terminal pins 101a and 101b extend through the stem base 103. The CRT socket is attached to the CRT to electrically connect to the focusing terminal pins 101a and 101b. A single barrier wall 233, made of resin, is interposed between the end of the first focusing terminal pin 101a and the end of the second focusing terminal pin 101b. 
When a high dynamic voltage is applied to one of the focusing terminal pins 101a and 101b, the resin barrier wall acts as an inductor. This results in the generation of a corona current that causes discoloration and deterioration in the resin barrier wall. This constitutes a technical problem for conventional devices.
Side walls 231a, 231b, 232a, 232b of the focusing terminal pin housing are also single walls. The gaps between these side walls and the focusing terminal pins are only about 0.4 mm at their narrowest points. Dust can adhere on these resin side walls of the housing and the walls may become moist, resulting in the side walls acting as an inductor. As above, a corona current flows through the side walls causing discoloration and deterioration in the resin forming the walls. This also constitutes a technical problem for conventional devices.
It is an object of the present invention to provide a CRT socket that overcomes the drawbacks of the prior art.
It is a further object of the invention to provide a construction of a CRT socket that is effective in preventing the generation of corona currents between the two focusing terminal pins in a double focus tube and between a focusing terminal pin and the surrounding insulating resin wall.
A CRT socket according to a first aspect of the present invention includes: a ring-shaped portion that has a cylindrical central hole passing therethrough from a front face to a rear face thereof and signal connecting means which is positioned approximately concentrically with and on an outside of the cylindrical central hole and engages signal terminal pins of a CRT; a cover portion equipped with high voltage connecting means disposed approximately concentrically with the cylindrical central hole and which engages each of two focusing terminal pins of the CRT; and a base portion that corresponds to a rear face of the cover portion, wherein at least two insulating walls are interposed between the ends of the two focusing terminal pins.
With the above construction, at least two insulating resin walls, with an air layer between, are interposed between the ends of the two focusing terminal pins. This means that the path between the two focusing terminal pins must pass through at least one air layer between the two walls. Air has a substantially lower dielectric constant than the resin walls. Accordingly, even if a dynamic high voltage is applied to one of the two focusing terminal pins, the chance of generating a corona current is very small.
A construction with two or more insulating resin walls can be realized in a number of conceivable ways. As a first example, a channel is formed in a barrier wall on the cover portion, with a barrier wall on the base portion fitting into this channel to form a triple-wall construction, as shown in FIGS. 4A and 4B. This offers two air barriers between the two focus terminal pins. In another example, a channel is formed in a barrier wall of the base portion, with a barrier wall on the cover portion fitting into this channel to form a triple-wall construction, as shown in FIGS. 7A and 7B.
A CRT socket according to a second aspect of the present invention includes: a ring-shaped portion that has a cylindrical central hole passing therethrough from a front face to a rear face thereof and signal connecting means which is provided approximately concentrically with and on an outside of the cylindrical central hole and engages signal terminal pins of a CRT; a cover portion equipped with high voltage connecting means that is provided approximately concentrically with the cylindrical central hole and engages a focusing terminal pin of the CRT; and a base portion that is provided so as to correspond to a rear face of the cover portion, wherein a cover-side focusing terminal pin housing is provided in the cover portion and a base-side focusing terminal pin housing is provided in the base portion so as to engage the cover-side focusing terminal pin housing, the housing having at least double insulating side walls that separate the end of the focusing terminal pin from the outside.
With the above construction, at least one extra wall is provided at the narrowest part of the gap between the side wall forming the housing for the end of a focusing terminal pin and the focusing terminal pin itself, so that the focusing terminal pin is surrounded by at least two walls. As a result, even if dust adheres on the outer wall and the outer wall becomes moist, a layer of air with a low dielectric constant is formed between the two walls thereby preventing the generation of corona currents.
A construction where the side walls of the housing have at least a double-wall construction can be achieved as shown in FIGS. 4A and 4B where a side wall formed on the cover portion engages a side wall formed on the base portion to form a double-wall construction, or as shown in FIGS. 7A and 7B where two walls are integrally formed on the base.
A CRT socket according to a third aspect of the present invention includes: a ring-shaped portion that has a cylindrical central hole passing therethrough from a front face to a rear face thereof and signal connecting means approximately concentric with, and on an outside of, the cylindrical central hole and engages signal terminal pins of a CRT; a cover portion equipped with high voltage connecting means that is provided approximately concentrically with the cylindrical central hole and engages a focusing terminal pin of the CRT; and a base portion that is provided so as to correspond to a rear face of the cover portion, wherein a base-side focusing terminal pin housing is provided in the base portion and a gap of at least 1.0 mm is left between the end of the focusing terminal pin and side walls and a bottom of the base-side focusing terminal pin housing.
In a conventional socket, corona currents can easily occur due to the narrow (0.4 mm) gap between the end of a focusing terminal pin and the side walls of the housing. With the present invention, a gap of at least 1.0 mm, and preferably at least 1.5 mm, is left between the end of a focusing terminal pin and the bottom and side walls of the housing. Since air has a low dielectric constant, this extra distance is effective in preventing the generation of corona currents.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.